This article reviews the demographic effects of breastfeeding on fertility and child survival and, ultimately, on population growth. Extended breastfeeding both reduces fertility by prolonging birth intervals and increases child survival through improved nutrition, especially where adequate substitutes are not available. The results presented show, however, that although breastfeeding is a major determinant of fertility in the absence of other means of fertility control, prolonged breastfeeding alone cannot reduce fertility to levels consonant with slow or zero population growth. The benefits, at least for the first year of life, demonstrate the need for policies that promote breastfeeding and encourage compatibility between breastfeeding and other aspects of women's fives. In particular, policies are needed that permit women to breastfeed their children while, at the same time, improving their socio-economic circumstances through participation in the labour force.